This invention relates to optical scanning, e.g., scanners for reading bar codes.
Targets having indicia of different light reflectivity, such as bar code symbols, have been scanned by directing a laser beam along an optical path to a symbol located in the vicinity of the reference plane lying generally normal to the optical path. The laser light reflected off the symbol is detected by a detector having a finite field of view or scanning field.
In the case of hand-held scanners, a scanner must be manually positioned relative to an object having a symbol in such a way as to ensure that the scanner's scanning field encompasses the symbol (or enough of the symbol to enable its decoding).
In many applications it is desirable to provide hands-free scanner operation, for example, in point-of-sale check-out systems of the type generally found in supermarkets. Hands-free operation is achieved in a number of ways. For example, in the case of point-of-sale checkout systems, it is well-known to mount symbol scanners underneath check-out counters. (See, for example, U.S. Pat. No. 3,978,317.) Portable, hand-held scanners can also be temporarily mounted (e.g., in a mounting stand as is shown in U.S. Pat. No. 4,766,297).
To scan a symbol using fixed-position or temporarily mounted scanner environments, the object having the symbol to be scanned must be manually positioned relative to the fixed-position scanner in order to move the symbol into the scanner's field of view.
Scanners with fixed-position fields of view have been mounted on vertical walls, to facilitate hands-free scanning of objects moved under them. The light beam emitted by such wall-mounted scanners is angled outwardly from the wall, in an effort to position the field of view far enough away from the wall to provide enough maneuvering room in which to move objects so that the indicia to be scanned can be brought within the field of view.